1. Field of the Invention
This invention relates to the field of seating systems and more particularly, to the field of anti-decubitus seating systems for wheelchairs for reducing the development of pressure sores.
2. Discussion of the Background
As set forth in the prior invention of U.S. Pat. No. 5,352,023, growing children present a unique problem to seating and back systems for wheelchairs in that the fitting requirements of the child are continually changing sometimes on a month-to-month basis. The basic objective of such pediatric seating and positioning systems is to maintain the pelvic and spinal alignments to a desired configuration so that normal growth may occur without risk of permanent physical deformity. Children are more prone to skeletal deformities because their bones are soft and are very susceptible to being pulled into permanent deformities, particularly during growth spurts. The previous invention of U.S. Pat. No. 5,352,023 disclosed a seat and back structure that was essentially adjustable in numerous aspects so that the positioning requirements of the growing user could be continually met throughout a period of growth. The present invention is directed to further improving the capabilities of the seating system by substantially improving the pressure relieving qualities of the fluid bladder or pad component of the previous invention of U.S. Pat. No. 5,352,023.
Research has shown that most pediatric wheelchair bound users are not substantially at risk for decubitus ulcers (pressure sores, bed sores). This is true primarily because the diagnoses do not involve the loss of sensation in the lower extermities as would for example spinal cord injuries. However, there are some instances where the diseases (e.g., cerebral palsy and spina-bifida) have progressed to the point where sensation is impaired and the user requires a seating system that not only maintains the appropriate pelvic alignment but also provides a quality of pressure and shear relief to the underlying soft tissue of the user. In the past, most of the fluid--filled, pressure-relieving bladder configurations have employed oversized fluid segments or pouches that are bunched or gathered into a defined seating well. The excess bladder material serves a dual purpose in that it prevents hammocking of the bladder membranes or covers and also provides the necessary stroke or displacement tangentially to the fluid support surface so that shear forces on the supported body are kept at a minimum. The prior use of these types of fluid bladders has proven to be very successful when applied to cushion bases or trays where the user's position on the cushion is predictable (i.e., hips to the back and centered). Furthermore, in these prior applications, it was assumed that the majority of the fluid pad would be in contact with the user and thus the need to restrain certain portions of the bladder from ballooning or billowing around the user was not required. The ballooning or billowing described is detrimental to the function of the fluid pad because the supporting fluid volume would then be allowed to accumulate in these ballooning volumes. This would cause the user to sink farther into the cushion and eventually bottom out on the underlying rigid foam tray of the cushion structure.
The adjustable growth cushion described in the previous invention of U.S. Pat. No. 5,352,023 inherently creates a condition where there are unsupported or unused portions of the fluid pad. This previous invention employed a fluid pad that was segmented into several pouches on each side of the cushion centerline. This segmenting prevents the detrimental fluid migration from underneath the user if the user is indeed sitting on only the front half of the cushion surface. This configuration is an appropriate solution for when the fluid bladder is required to provide only a limited amount of pressure relief and little or no shear relief. Improved pressure and shear relief may be achieved in this prior invention by introducing more fluid to the seating well area. However, simply oversizing the fluid bladder of this previous invention relative to the underlying tray structure would not be a particularly effective solution because the unsupported areas of the fluid pad would accumulate fluid volume and allow the user to bottom out.
The fluid bladder or pad of the present invention overcomes the problems discussed above. Among other things, it does so by oversizing the top or canopy portion of the outer covers of the fluid pouches in a vertical direction normal to the tray support surface. Furthermore, the fluid pad of the present invention cooperates with the underlying foam tray by the incorporation of three-dimensional, geometrically configured fluid pouches that correspond to the general contours of the depressed seating well of the underlying tray. The resulting configuration is thus capable of satisfying all of the requirements of pressure relief, shear relief, and growth accommodation.